I just completed a very successful hatch ( of the 50 that went into lockdown only 6 didn't make it). The 2 hatches I had before this one all my chicks died in the shell. The reason being: not enough air flow, too high humidity and too many temp spikes. This time I kept my temps between 100.9 and 102.3 and I didn't add water during the first 18 days. I filled up both water troughs in my incubator and added 2 wash clothes and kept my humidity between 50-60% during lockdown. It spiked up to 70% a few times after the chicks started hatching. These temps and humidity may not work for everyone but for me it was a very good hatch rate. I have 3 little giant still air incubators with no turners.
ChooksChick has a really good cheat sheet on her profile which really helped improve my hatches.